This invention relates generally to piezoelectric actuators and, more specifically, to a prestressed piezoelectric actuator having an integral lead.
Piezoelectric devices, such as piezoelectric benders or actuators, generally consist of a piezoelectric material that deforms when an electric field is applied across it. Additional materials may be bonded with the piezoelectric material, such as metallic layers that act as electrodes, insulating materials to prevent current from flowing between particular areas of the device, and adhesives to bond the various layers together.
A typical piezoelectric device, such as a piezoelectric bender, may be comprised of an electroactive layer, such as various types of ceramics, disposed between a reinforcing layer and a top or conductive layer, although other configurations, such as electroplating, are also possible. The bender may be pre-stressed by ways known to those skilled in the art to have a domed, or arcuate, configuration.
A representative pre-stressed piezoelectric bender is seen in U.S. Pat. No. 5,632,841. The bender is a composite structure constructed with a piezoelectric ceramic layer which is electroplated on its two major faces. A metal reinforcing layer is adhered to the electroplated surface on at least one side of the ceramic layer by an adhesive layer. During manufacture of the bender, the ceramic layer, the adhesive layer and the reinforcing layer are simultaneously heated to a temperature above the melting point of the adhesive, and then subsequently allowed to cool, thereby re-solidifying and setting the adhesive layer. During the cooling process the ceramic layer becomes strained and deforms in an arcuate shape having a normally concave face due to the higher coefficients of thermal contraction of the reinforcing layer and the adhesive layer than of the ceramic layer.
In conjunction with the bender disclosed by U.S. Pat. No. 5,632,841, or with other benders, whether thermally, mechanically or otherwise prestressed, it is also generally known in the art to provide a top layer of an aluminum material adhered to the ceramic layer to protect the ceramic and assist in controlling the amount of pre-stressing present in the ceramic layer. Aluminum, which is a relatively inexpensive material, has a modulus of elasticity (or Young""s modulus) which may be greater than or similar to the modulus of the ceramic material; thus, providing an aluminum top layer increases the stiffness of the bender and limits the doming of the bender. In addition, the aluminum layer may act as a protective cover for the ceramic layer and for any leads adhered to the ceramic layer. Conductive leads, which supply the necessary voltage to the ceramic, are typically adhered to the ceramic layer under the aluminum layer. However, due to the differing thickness within the bender from the adhered lead, stress may accumulate in the area of the adhered lead, and this area may be a point of failure of the bender.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In a first embodiment, a piezoelectric bender is disclosed, the bender comprising at least one layer of an electrically active ceramic, at least one layer of a copper material, and at least one layer of a substrate, wherein the ceramic layer is disposed between the copper layer and the substrate layer.
In a second embodiment, a piezoelectric bender is disclosed, the bender comprising a first layer having a plurality of apertures defined therein and a second layer adhered to the first layer.
In a third embodiment, a piezoelectric bender is disclosed, the bender comprising a first layer having a lead formed integrally therewith and a second layer adhered to the first layer.
These and other aspects and advantages associated with the present invention will become apparent to those skilled in the art upon reading the following detailed description in connection with the drawings and appended claims.